Light emitting diodes (LEDs) have been used for decades in applications requiring relatively low-energy indicator lamps, numerical readouts, and the like. In recent years, however, the brightness and power of individual LEDs has increased substantially, resulting in the availability of 1 watt and 5 watt devices.
While small, LEDs exhibit a high efficacy and life expectancy as compared to traditional lighting products. A typical incandescent bulb has an efficacy of 10 to 12 lumens per watt, and lasts for about 1,000 to 2,000 hours; a general fluorescent bulb has an efficacy of 40 to 80 lumens per watt, and lasts for 10,000 to 20,000 hours; a typical halogen bulb has an efficacy of 20 lumens and lasts for 2,000 to 3,000 hours. In contrast, red-orange LEDs can emit 55 lumens per watt with a life-expectancy of about 100,000 hours.
Because LED devices generate heat, the use of LEDs or LED lamps in a recessed can fixture or housing can present problems due to the thermal constraints of LEDs—heat negatively affects the optical and electrical performance of LEDs. Because conventional recessed can applications tend to be thermally inefficient and do not provide adequate heat ventilation, an LED device installed into a recessed can housing will quickly generate substantial amounts of heat within the housing that can damage the device.
Presently, most of the recessed can housings for residential and commercial applications are fully sealed at the can top, which means there is no air passage from the can to the space above the housing. Also, in most cases, the thermal insulation in the attic is placed around the can further restricting the flow of heat out of the housing. As a result, there is no effective heat dissipation path from the can housing to the attic.
An LED-based lamp installed into a recessed can housing requires an effective heat dissipation path to operate and to maintain its optical and electrical performance, longevity and reliability. FIG. 1 is an illustration of an LED parabolic aluminized reflector (PAR) lamp with a conventional base socket that may be installed into a conventional recessed can housing. Although the fins on the lamp are designed for dispersing the heat generated from the LED light engine, the heat is captured within the housing and does not dissipate. Lab experiments show that the fin temperature of a 15 watt LED lamp operated under open air conditions generates a rise in fin temperature of 25° C. over ambient temperature. When the lamp is positioned flush with the lid of a recessed can housing there is a 45° C. rise over ambient air temperature in the housing. If the lamp is further recessed into the can 2.54 cm behind the can lid, the temperature increase is approximately 60° C. At the ceiling of a typical home the air temperature will be 40° C. in the summer. As a result, the LED die junction temperature inside the LED lamp may be over approximately 100° C. when the LED lamp is flush with the trim lid.
The recessed can is one of the most widely used light fixtures in modern homes in the United States. There are millions of incandescent light bulbs installed into recessed can fixtures. Successful retrofit of an LED lamp to the existing and new recessed can housings may result in an 80% decrease in lighting energy consumption and an increase of the lamp's operating life from a typical 2,000 hours incandescence to the 50,000 hours of an LED device.